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Sunday, 17 July 2011

Which frigatebird?

Comments are welcome on the identity of this frigatebird, photographed on Michaelmas Cay in the Great Barrier Reef, Queensland, Australia, in early August 2009.

Having recently researched birding information on Queensland for an article in next month's Birdwatch, I was reminded of a minor identification puzzle from my first visit to Australia two summers ago. One of the highlights of that holiday was visiting the Great Barrier Reef, a long-held ambition. We made two trips, and for the first my son Ed and I took a boat out from Cairns to Michaelmas Cay, where we did some snorkelling and enjoyed the company of large numbers of Great Crested and Sooty Terns and Brown Noddies.

The dark head and throat suggest Lesser Frigatebird, though that species should typically show a more pointed white 'spur' on the axillaries, with the black on the lower underparts protruding more into the white breast.

While photographing the throng of terns on the beach, a lone frigatebird drfited over. My previous experience of this family was restricted to Magnificent Frigatebird, so I was immediately out of my comfort zone. Both Great and Lesser Frigatebirds occur in the Great Barrier Reef, the latter apparently more commonly, but I haven't felt fully confident nailing this bird as either species. The dark head and throat are strongly suggestive of Lesser, but the white breast doesn't appear to extend as a 'spur' onto the axillaries in the typical way shown in photos and illustrations of Lesser, and neither does the black on the lower underparts terminate "in inverted V at white breast", as Harrison puts it (and illustrates it) in Seabirds: an Identification Guide. Plate 52 in that work also depicts adult female Lesser as having the black head almost isolated from the dark upperparts by a near-complete narrow white collar, which clearly isn't the case here either (perhaps making it a sub-adult?).

Seeking closure on the ID, I emailed images to a friend in Queensland for comment. To my surprise, he felt unsure too, so here I throw the question open to anyone who feels suitably qualified to give a firmer view. Doubtless it's more straightforward for those with frequent experience of both species, so I look forward to learning.

In the meantime, here's a few more images from that trip to Michaelmas Cay:

Thanks for the feedback, Tim. No firm IDs were received in response to a post on the bird on Seabird-News, so it doesn't appear to be a straightforward individual. I emailed the author of that Birding Asia paper a while ago, but the message bounced back and I haven't been able to trace a new email address.